1. Field of the Invention
The present invention relates generally to a gas-and-water-tight elongated flexible fastener used on water-proof bags, water-proof canvases, raintight cover and the like and particularly to a gas-and-water-tight elongated flexible fastener comprising an elongated plug and an elongated socket which can be firmly coupled together so that the fastener is improved in gas-and-water-tightness.
2. Description of the Prior Art
There are two types of gas-and-water-tight elongated flexible fasteners described above. The first type is disclosed in Japanese Patent Publication No. 37-12467. This type of fastener comprises a plug and a socket adapted to be coupled together. The elongated plug has a coupling head adapted for coupling engagement with the socket and having an elongated inner hollow formed thereon. The elongated socket has a coupling groove adapted for coupling engagement with the coupling head of the plug and an elongated inner hollow formed behind the coupling groove. Since the coupling head and the coupling groove are generally round in contour, the fastener itself does not provide sufficient gas-and-water-tightness. For sufficient gas-and-water-tightness, both inner hollows of the socket and plug must be supplied and inflated with pressurized fluid after the coupling head of the plug comes into coupling engagement with the coupling groove of the socket, thereby swelling the coupling head and contracting the coupling groove so that the head-and-groove coupling engagement becomes the tighter and the fastener enjoys increased gas-and-water-tightness.
The second type of fastener is disclosed in Japanese Utility Model Publication No. 4-3965. The second type of fastener comprises an arrow-shaped plug and a socket to be coupled therewith. The plug has an arrow-head-shaped head which in turn has a pair of locking fins formed on its opposed sides. The socket has a pair of symmetrical hook portions facing each other to define therebetween a coupling groove. The hook portions terminate with the respective hook ends which face each other. In addition, the hook portions have at the middle portions their respective tongues projecting toward each other. The head of the plug is thrusted into the groove of the socket until the opposed locking fins of the plug comes into locking engagement with the respective hook ends of the socket with the projecting tongues resting against the opposed sides of the plug head so that the fastener enjoys gas-and-water-tightness.
However, the above-mentioned two types of fasteners suffer from the respective drawbacks.
In the first type of fastener, for sufficient gas-and-water-tightness, both inner hollows of the socket and plug must be supplied and inflated with pressurized fluid after the coupling head of the plug comes into coupling engagement with the coupling groove of the socket, as mentioned earlier. This makes the coupling operation tedious and time-consuming. Not only this, the inflation of pressurized air into the inner hollow renders the plug and socket extremely stiff, thereby making difficult the manipulation of the fastener.
In the second type of fastener, when the plug are trusted into coupling engagement with the socket, the opposed locking fins of the plug comes into locking engagement with the respective hook ends of the socket with the projecting tongues resting against the opposed sides of the plug head so that the fastener enjoys gas-and-water-tightness, as mentioned hereinabove. However, the projecting tongues are deficient in urging the head of the plug outward, so that the fastener could lose gas-and-water-tightness depending on how severely the fastener is used. For example, if the fastener is subjected to severe distortion or other severe stresses, the fastener is very likely to lose gas-and-water-tightness.